It has nothing to do with how tight the building is. You must provide an amount of air to dilute chemicals in the home and keep Co2 levels at bay. You can't determine what is in the air being breathed coming from exterior cavities in walls. Reason you need air filtered from outside has to do with it can be up to 100 times less polluted than Indoor air.You can have the best filtration in the world to remove particles inside the home but without the 1/3air change you will run into healthy home Issues, this includes high moisture. Yes there is a slight sacrifice in heating and AC but you can't just concentrate on Energy and sacrifice health.

Oddly 98% of homes do not have either, most home get enough air changes through leakage. If mechanical ventilation was that important it would be code. Outside of the Building Science/HVAC world 98% of the population doesn't even know what an HRV or ERV is, much less actually seen one.

It is code where I am from and let me tell you if a house is leaky then you are breathing the crap that comes in from the exterior walls. Not healthy. Granted I do understand in US why this might be a problem to digest as many days are very hot and adding heat and moisture to a home without proper control is a disaster waiting to happen. It is even more critical in Commercial applications.

Few residential customers care enough to pay for ventilation technology to be installed. IAQ would be much improved by air-sealing and ductwork repair, yet few are willing to pay for it. Even if it were to become code tomorrow it would take years before homes all had this done.

Ideal homes (Builder in our area) is the only one that is doing anything about IAQ. They install a aircycler that runs the blower every 20 minutes.

In the commercial installations economizers are part of RTU's, but are rarely setup correctly and often bypassed altogether.

Bob we have the strictest requirements just put in place in Ontario in the new Ontario Building Code 2006 and it applies to all homes from 2012 and up. This is also going to be put in place in all Commercial buildings soon after 2013.You are correct about the economizer and it is part of the problem. So to solve the problem a new way is being introduced to separate the fresh air requirements and circulated with HRV or ERV for commercial applications plus chilled or heated beams.

Code is very lax in Oklahoma. It isn't uncommon to find straight electric resistance heat as a primary heat source for a home. Yes it's expensive to run, but it's cheap for builders to install. Most parts of the country cringe at the idea if a 20KW air handler being the primary heat source for a house. The people building the house are more concerned with the granite counter tops than spending an extra $1,000 or so to get a heat pump..

The HEPA aspect however, I respectfully do not put much weight on that. Properly applied, HEPA filtration has its place, but to be effective at all requires far more air changes than you want in a house. Yes, they capture fine particles but they also load up without good ("cannot see through them") pre-filters to prolong their lives.

I have designed clean rooms down to Class 1 but even Class 1000 requires dozens of air changes per hour to be effective; in a typical application, the entire ceiling was HEPA modules with a downward piston of air at 90 feet per minute as an example.

Point being, you are talking less than half an air change per hour in a typical house, often much less. The degree at which people, pets and living generate particulates far exceeds that air change and filtration rate's ability to remove them.

A good MERV-8 filter maybe followed by a MERV-13 filter will do as much good for less cost, even considering that you are not "polishing" (recirculating) the air, which is what most clean rooms do, using very little outside air.

Seems like a number of discussions going in a single thread. In an increasing number of homes, mechanical ventilation is necessary. Relying on natural leakage to provide adequate pollution dilution in the house generally means that on AVERAGE the house is adequately ventilated throughout the year. That means that half the time it is over ventilated and half the time it is under ventilated. One complete air change in a house with a static pollution source like a Limburger cheese on the kitchen counter, will dilute the air by 50%. 2 air changes - 25%. etc. It takes a lot of air changes even with a static or constant source.

Increasing the filtration on the air handler shouldn't be done without measuring the total external static pressure of the system and comparing it to the performance curve of the blower. The higher density filters can greatly impact the performance of the system.

HRVs and ERVs are meant to be balanced - equal amounts of air on both sides. That's the way they are certified at HVIs performance laboratory. (Check out:HVI Product Directory) If they are operated in an unbalanced condition, they will impact the performance of the house. Greater supply flow will put the house under positive pressure which may drive moisture into the walls in a heating dominated climate. Greater exhaust flow will put the house under negative pressure, possibly sucking moisture into the walls in a cooling dominated climate.

HRVs and ERVs are great products, but their design and installation have to be done carefully. They most definitely need to be located in a place where the occupants have access to the filters for maintenance.